For the examination of paper, which may be described as a “felt of finely divided fibres,” the microscope is invaluable. The essentials of a good paper are that it be durable, that it retain its colour and not become brittle. The least observant of us cannot fail to have noticed that there are an extraordinary number of different kinds of paper, not only the many kinds which the paper manufacturers could show us, but the obviously varied papers which we meet with every day. Added to the papers, there are cardboards which are really a kind of paper. It is clear, therefore, that the man who can tell us exactly how any and every paper is made and what it is made of has laid up a goodly store of knowledge. In carrying out tests of paper we rely partly on chemical and partly on microscopic tests. A number of substances contribute to the manufacture of paper; linen and cotton rags, hemp and various fibres are the most commonly used, not forgetting wood pulp which we shall mention in a moment. The finest and whitest paper is made from linen rags and that from unused linen and hemp is the strongest. Without attempting to describe in detail or even in outline the different processes which the various vegetable fibres must undergo before they appear in the guise of paper, we may say the treatment is very drastic. Strong chemicals and machinery designed to reduce the fibre to the finest possible particles render the examination of paper, for the purpose of discovering its composition, far from easy. Such fibres as survive the rough treatment are mere fragments yet they are often large enough for the lynx eyed microscope to read their story. Formerly the constituents of most papers could be separated into three classes according to their behaviour with iodine solution, but this test has been superseded by more complicated methods which do not concern us here. The examination of various papers may prove interesting for example in linen rag paper, we ought to find some flax fibres, they will be sadly battered and torn but are usually recognisable under the microscope. Hemp paper is tough and is used for bank notes, in it some of the short tow fibres will probably occur and they will give a clue to its composition. Cotton rag paper is easily recognised for the fibres are very characteristic, a remark which also applies to jute paper, the so-called manila used for envelopes, wrappers, etc.